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BIIB · Biogen Inc. · Holdings

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$243.22 +9.74 (+4.17%)
Market Cap
$34.77B
Shares
147.64M
Volume · Oct 20 492.66K Avg daily vol (3M) 997.42K

Institutional ownership from SEC Form 13F filings. Investment managers with more than $100 million in U.S. equities must disclose their positions every quarter, within 45 days of quarter-end, so the holdings shown can lag the market by up to a quarter.

Institutional holdings are being reconciled with SEC filings. Holder totals and changes may be incomplete until reconciliation finishes.
The Sep 30, 2026 filing window is still open — showing the latest known positions. Funds that have not filed yet carry their prior-quarter positions; a fund that filed without this stock counts as sold out. Each fund's Change is measured against its own previous reported quarter, shown in the Reported column. Pick a completed quarter in the Quarter selector below to put every fund on one quarter and see the stock-wide activity breakdown.
Holders: 1,063
Total Value: $31,779,794,562
Total Shares: 147,123,829
Showing 1–100 of 1,107 holdings by value · page 1 of 12

Institutional Ownership Trend

27 quarters

Holder Concentration

Across 1,057 13F filers
Top Holder
12.4%
Sep 2023 → Jun 2026 · range 11.6% – 12.8%
of institutional value
Top 5
45.2%
Sep 2023 → Jun 2026 · range 42.3% – 46.3%
of institutional value
Top 10
58.2%
Sep 2023 → Jun 2026 · range 53.7% – 59.3%
of institutional value
HHI
508
Sep 2023 → Jun 2026 · range 468 – 556
Broadly held

Who Holds BIIB

Last 8 quarters through Sep 30, 2026 (filing window open)

Each kind of 13F filer's share of the common shares 13F filers report. Holder type comes from regulatory records, never the filer's name; style, turnover and horizon are measured from each filer's own 13F book. The quarter selector does not change this card.

Jun 30, 2026, the newest closed quarter: 1,048 filers, like-for-like change +3.6%; actively managed books +5.1%; index-like books +1.2%.

Holder type Share Filers Change
Registered adviser 39.7% 567 -2.2%
Exempt adviser 0.1% 6 -75.6%
Adviser 1.7% 16 -28.9%
Bank 11.4% 40 +3.7%
Insurer 0.3% 4 -18.7%
Broker-dealer 0.1% 2 +0.3%
Benefit plan 0.2% 6 +52.9%
Non-US 3.9% 13 -4.2%
Holding company 29.1% 11 +18.6%
Registered fund 0.0% 0 —
Unknown 13.6% 383 +3.3%

The Sep 30, 2026 filing window is still open, so its bar carries the Jun 30, 2026 positions of filers that have not filed yet.

How the mix is measured

Shares are 13F common shares restated to today's split basis; options and principal amounts are left out. The change compares only filers with a 13F in both quarters and keeps each filer in its bucket of the later quarter on both sides; a filer that continues under a new CIK is compared through its successor. Holder type comes from each filer's current regulatory profile; client base and private funds come from the Form ADV roster current at each quarter end (rosters from December 2019, so an earlier quarter reads Unknown). Style, turnover, horizon and book size are measured from each filer's 13F book in the newest measured quarter, and Not measured means none was. Actively managed books are those measured systematic-like, concentrated or diversified active.

Excluded 14 holders with no observed 2026-03-31 13F and 10 holders with no observed 2026-06-30 13F. Compared across CIK changes: JANUS HENDERSON GROUP PLC continues as Jupiter Topco LLC.

Fund Ownership of BIIB by Fund Type

Registered funds' Form N-PORT reports for the quarter ended Jun 30, 2026

Index funds and index ETFs hold 22.93% of shares outstanding.

Fund type Of shares outstanding Shares
Index funds 4.87% 7,187,807
Index ETFs 18.07% 26,672,132
Active ETFs 0.49% 727,909
Active funds 23.99% 35,416,966
Unclassified 1.33% 1,964,325
All registered funds 48.75% 71,969,139
How fund types are measured

Each fund series counts once, with its latest Form N-PORT report dated inside the quarter; only long share positions count, restated to today's split basis. The fund type is the series' latest Form N-CEN answer on or before the quarter end (the index-fund box and the exchange-traded flag), never its name. Unclassified funds have no usable N-CEN; unit investment trusts are among them, so index ownership is a floor. Funds sit inside their advisers' 13F reports, so these shares overlap the 13F figures and are never added to them.

Showing 100 of 1,107
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Holder Value (USD) % of 13F Shares Open

Showing the top 100 of 1,107 holders. Create a free account to see every holder, past quarters, search, filters and CSV export.

Key facts CIK 875045 CUSIP 09062X103 13F (30d) 163 filings 148 filers Visit website Investor relations